(303f) A Reactive Molecular Dynamics Research for the Effect of Strain Energy On Hydrolysis Reaction of the Silica-Water Interface
AIChE Annual Meeting
Tuesday, November 5, 2013 - 1:45pm to 2:00pm
We performed reactive force field MD simulation to observe the hydrolysis reactions between water molecules and locally strained Si geometry. We established that the ReaxFF potential used in this research accurately describes the water - silica hydrolysis reaction by comparison with DFT data. Number density of silanol-grouups on the surface and properties of the vitreous silica slab obrained from ReaxFF simulation are consistent with experimental results. We demonstrate that the reaction barrier for silanol formation in strained geometry is significantly less than that for non-strained sites. Observation of silanol formation at the high-strain region of a silica nano-rod also supports the concept that the adsorption of water molecule and hydroxyl formation favors the geometry with higher strain energy. Formation of surface hydroxyl in amorphous silica double slit displays a similar tendency: SiOH formation prefers high-strain sites. The most frequent way of surface hydroxyl formation was dissociation of an adsorbed water molecule, creating 2 SiOH on the surface. In addition, we observed proton transfer and proton hopping through the interface, which is also responsible for SiOH formation. A third mechanism observed from our simulation is water or hydronium molecule donating a proton to the surface dangling oxygen, or strained bridge oxygen. This result implies that hydrolysis reaction with water molecules on the silica surface prefers the strained sites of the surface. In addition, we expect that this strain energy - hydrolysis relationship on the surface are relevant to tribology research, as it enable us to predict the attachment points of the lubrication film to the silica surface.